System for arbitrary antenna polarization control



G. E. HART Dec. v5, 1967 SYSTEM FOR ARBITRARY ANTENNA POLARIZATION CONTROL Filed Feb. 26. 1954 x Q mt); xom \B mw Em om xom $33 I. 528mm F mm E 595322 6 vm 3 2 X0@ mwizzw xom E wmii E A 39532 A mm wN NN Q ON on mlk V NN E 5 a F hm l 9 xom 3 wk 3. Q EEEm .5 ww $35 595322 mm {v mm xom mwiiw xom. in g (m k 04 wm N mm xOm w;

w wig ORNEYj United States Patent 3,357,013 SYSTEM FOR ARBITRARY ANTENNA POLARIZATION CONTRDL Gerald E. Hart, Naval Research Laboratory, Washington, DC. 211390 Filed Feb. 26, 1954, Ser. No. 412,964 7 Claims. (Cl. 343-) This invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The invention relates to apparatus for propagating and receiving electromagnetic waves having various types of polarization.

More specifically this invention relates to apparatus for propagating electromagnetic waves having any type of plane, circular or elliptical polarization characteristic and for receiving any type of polarization and the orthogonal or cross-polarized component of such other received polarization.

It has been found that the characteristics of radar targets may be more easily determined by increasing the variables subject to change in the reflection of a transmitted pulse. By controlling the polarization of the transmitted wave and detecting the polarization characteristics of the reflected wave it is possible to resolve targets which might otherwise be indistinguishable because of noise, interference and clutter reflections. In addition to distinguishing the target from the background, the reflected polarization indicates the nature or characteristic of the surface or geometry of the target. The invention represents an improvement over the device disclosed in US. Patent No. 2,619,633 issued November 25, 1952 to H. N. Chait.

One object of this invention therefore is to provide apparatus for transmitting any type of plane, circularly or elliptically polarized electromagnetic waves.

Another object of this invention is to provide apparatus for receiving any type of plane, circularly or elliptically polarized electromagnetic waves and their cross-polarized components independent of the polarization of the transmitted wave.

Another object of this invention is to provide apparatus for transmitting and receiving plane polarized electromagnetic waves of any desired polarization orientation while employing fixed antenna elements.

Another object of this invention is to provide apparatus for transmitting and receiving elliptically polarized electromagnetic waves of any desired ellipticity, major axis orientation and rotational sense while employing fixed antenna elements.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein:

FIGURE 1 is a diagram showing the the relationship of the various elements which make up the invention.

FIGURE 2 is a vector diagram showing the phase and amplitude relations of the electromagnetic waves produced in the apparatus of FIGURE 1.

FIGURE 3 is a representation of the polarization of a transmitted wave, its orthogonal or cross-polarized component and a single bounce reflected wave.

To produce any variation of linear, circular and elliptical polarization with any desired orientation in a horn antenna in which two feed probes are spaced from each other, it is necessairy to provide means for feeding the probes with signals of any selected amplitude ratio and time phase relation. The device of FIGURE 1 not only CAD provides for feeding such signals to the antenna probes but may also be adjusted to receive, independently of transmission, any other type of polarization desired plus the cross-polarized component of this received wave. This control of polarization in transmitting and receiving is accomplished by means of the four adjustable phase shifters shown in FIGURE 1. By means of these phase shifters, it is possible to tune for various polarizations of the transmitted and received signals without changing the orientation of the antenna elements.

There are three basic types of elecric field polarizaion which have been mentioned above and will now be discussed in greater detail; these types are linear, circular, and elliptical polarization. In linear or plane polarization, the electric field does not rotate as it does with circular and elliptical polarization. Circular polarization may be characterized by rotation of the electric field in space while remaining constant in magnitude. In elliptical polarization the vector rotates and also changes in magnitude; the locus of points of the end of a vector representing this latter type of electric field polarization 'being an ellipse.

The cross-polarized component of a linear, horizontal, electric field polarization (i.e., electric field extending horizontally) is a linear vertical electric field polarization. An electric field rotating clockwise with a constant magnitude is the cross-polarized component of an electric field rotating ounter clockwise at constant magnitude. An electric field rotating clockwise wherein the locus of a vector representing it follows an ellipse whose major axis is in a first given direction is the cross-polarized component of an electric field rotating counter-clockwise wherein the locus of the vector representing the electric field describes an ellipse having the same ratio of major to minor axis but having the direction of the major axis in space quadrature with the previously mentioned major axis.

Referring to the diagram of FIGURE 1, the elements necessary to change an electromagnetic pulse produced by transmitter 12 into an electromagnetic signal of any desired polarization transmitted from horn antenna 13 are shown in their function relationship. The arrows shown in the diagram indicate the path of the transmitted energy. Transmitter 12 is connected to the sum terminal 14 of the hybrid junction or magic-T 15 through a conventional ATR box 16. A TR box or switch is an electronic device normally employed to protect the radar receiver from damage by the large power of the transmitted pulses, by causing the line to the receiver to appear as a high impedance. Similarly, an anti-TR switch or ATR box is employed to improve efficiency by preventing received energy from entering the transmitter; this function is accomplished by causing the line to the transmitter to appear as a high impedance to the received pulse. TR and ATR boxes are employed in numerous instances in the embodiment of FIG. 1 to channel the received or transmitted pulse through selected phase shifters as will appear 1016 fully from the detailed description which follows. Throughout the specification and claims, the convention will be used designating the magic-T terminals as follows: terminal 14 as shown in FIG. 1 as the sum terminal; terminal 19 as the difference terminal; terminals 14 and 19 may be referred to collectively as symmertical terminals; and terminals 17 and 18 as symmertical terminals. This terminology which designates both pairs as symmetrical terminals is justified since they react similarly. That is, if energy is fed into terminal 19, half of this energy emerges from each of the terminal points 17 and 18, and none from 14. If energy is fed into terminal 18, half of this energy emerges from each of the terminal points 14 and 19, and none from 17. If equal amounts of energy are fed in time phase simultaneously to any pair of symmertical terminals, the sum total of the two :nergies will emerge from only one of the other symnetrical terminals.

The signal introduced into sum terminal 14 of the nagic-T 15 produces equal, in-phase outputs in the symnetrical terminals 17 and 18. Power transmission means 20 connects the symmetrical terminal 17 of magic-T 15 .0 one of the symmetrical terminals 21 of the second nagic-T 22. The other symmetrical terminal 18 of magic- 15 is connected by transmission means 23 and 24 to ATR box 25. Adjustable phase shifter 26 is connected be- ;ween ATR box and ATR box 27. Transmission means 28 and 29 connect ATR box 27 to the symmetrical terminal 30 of magic-T 22.

FIG. 2 is a vector representation of the voltage inputs and outputs of magic-T 22. The output of terminal 17 of magic-T 15 is designated as E, While the output of terminal 18 of magic-T 15 is E,,. As was stated above, the voltages E and E are in phase. The phase shifter 26 introduces a phase difference between the voltages B and E as received at symmetrical terminals 21 and 30. The outputs of the magic-T 22 are also shown in FIG. 2; the output of terminal 31, the difference terminal is designated as difference while the output of terminal 32, the sum terminal, as sum. It is apparent from FIG. 2 that the sum and difference voltages will always be 90 out of phase and that their relative magnitude will be a function of as determined by the setting of adjustable phase shifter 26. A more comprehensive analysis of the relationship between angle and the transmitted wave will appear below.

The output of difference terminal 31 is connected by transmission means 33 to the vertical probe 34 of the horn antenna 13. The output of the sum terminal 32 passes through transmission means 35 and 36 to ATR box 37. ATR boxes 37 and 38 isolate the phase shifter 39 from the circuit except as to the transmitted signal. The transmitted signal is passed from ATR box 38 through transmission means 40 and 41 to the horizontal probe 42 of the horn antenna 13. The probes 34 and 42 are, therefore, oriented in space quadrature and, when no phase change is introduced in phase shifter 39, the probes will be energized by signals in time quadrature.

Before considering the function of the apparatus relative to received signals an analysis will be made of the synthesis of the transmitted Waves of various types. Any desired polarization may be obtained by controlling the amplitude ratio and phase relation of the signals on the two probes 34 and 42 in the antenna feed. It is apparent that phase shifter 39 controls the phase relationship of the signals transmitted from probes 34 and 42. The phase shift introduced by phase shifter 39 will be referred to as angle There are various conditions of amplitude and phase to be met to produce the various types of polarization. For plane or linear polarization, the probes 34 and 42 must be energized by signals in time phase or 180 out of phase. Since determines the phase relationship of the energy at the probes and the signals produced from terminals 31 and 32 of magic-T 22 are 90 out of phase, phase shifter 39 must introduce a p of 90 or 270 phase shift to produce in phase or 180 out of phase operation respectively at the probes. Because of the 90 space phase of the probes, the plane of polarization, or E line plane, will be determined by the amplitude ratio of the two signals. Thus, referring to the diagram of FIG. 2, it is evident that for linear polarization the phase angle 4: introduced by phase shifter 26 would determine the angle which the plane of polarization makes with the horizon. This angle between the plane of polarization and the horizontal will be designated as 0. It can be shown mathematically that the ratio of the voltage on probe 34, the vertical probe, to the voltage on probe 42, the horizontal probe, is equal to:

The angle 0 may be given for in-phase operation as:

Combining the two equations we obtain:

for 180 out of phase operation Hence, for plane polarized operation the phase shifter 26 could be calibrated to indicate the angle 0 of the plane of polarization with the horizon.

Proceeding now to circular polarization, it becomes evident that the two antenna probes 34 and 42 must be energized out of time phase to produce any type of polarization other than plane polarization. Circular polarization, being a special case of elliptical polarization will be considered first. In circular polarization, the vector representing the magnitude and space position of the electric field remains constant in length and rotates either clockwise or counter-clockwise. To accomplish this function, the probes, when oriented in space position, must be energized by equal sinusoidal voltages which are 90 out of time phase with each other. The probe energized with the leading voltage determines the rotational sense; if the voltage on horizontal probe 42 leads, the rotational sense will be clockwise when looking outward from the antenna.

To produce such circular polarization, phase shifter 26 must be set for a 90 or 270 phase shift to give equal resultant signals from the sum terminal 32 and the difference terminal 31 of magic-T 22. It is clear from FIG. 2 that if were either 90 or 270 the sum and difference signals from hybrid junction 22 would be equal. Since it is desired that the probes 34 and 42 be energized 90 out of time phase and since the sum and difference signals from junction are 90 out of time phase, phase shifter 39 must be set to introduce no phase change. If it is desired to shift the rotational sense, a 180 phase shift can be introduced in phase shifters 39 or 26 to accomplish the change.

Under any conditions other than the special cases set forth above, elliptical polarization would be produced. By proper adjustment of phase shifters 26 and 39, any value of ellipticity (i.e., ratio of major axis to minor axis), orientation of the major axis, and sense of rotation can be transmitted. Thus if the phase shifter 26 were set for a 90 or 270 shift, varying the shifter 39 between 0 and 90 would result in elliptical polarization of an ellipticity ratio between one and infinity while the orientation of the major axis will be at 45 to the horizontal. To obtain other values of major axis orientation of the ellipse, different phase angles will have to be introduced in phase shifter 26 to obtain unequal magnitude signals at antenna probes 34 and 42 and thus establish a resultant at other than 45. A simple vector analysis of the requirements for complete flexibility will show that each of the phase shifters need introduce only -90 phase shift. By choice of the effective transmission line lengths 20 and 33 which are a quarter wavelength shorter than their parallel paths through the phase shifters, phase shifters capable of producing a 180 phase delay will produce an effective i90 phase shift.

The function of the apparatus on reception of any partlcula-r polarization is substantially the same as that of transmission except for the final production of two received signals which are the cross-polarized components. The vertical and horizontal components of the received electromagnetic wave are picked up by probles 34 and 42 respectively. The signal from probe 42 is transmitted through conducting means 41 and 43 to TR box 44. The output of TD box 44 is connected through an adjustable phase shifter 45 to another TR box 46. Transmission means 47 and 35 connect TR box 46 to the sum terminal of the hybrid junction 22. As was the case in transmission, the received signal from vertical probe 34 is conducted to the difference terminal 31 of hybrid junction 22 by transmission means 33. In like manner, transmission means 20 connects the output from symmetrical terminal 21 of hybrid junction 22 to the symmetrical terminal 17 of hybrid junction 15.

The remaining symmetrical terminal 30 of junction 22 is connected by transmission means 29 and 48 to TR box 45. Phase shifter 50 is isolated from the transmitted signals by the TR boxes 49 and 51. Transmission means 52 and 23 passes the received signal from TR box 51 to the symmetrical terminal 18 of magic-T 1'5. Receiver 2 is connected through the TR box 53 to the difference terminal 19 of hybrid junction 15. Receiver 1, in like manner, is connected through TR box 54 to the sum terminal 14 of hybrid junction 15.

It is evident that through the isolation of the parallel arranged phase shifters with TR and ATR boxes, the transmitted signal is operate-d on by an independent set of phase shifters over that which serves the received signal. If it were not for this feature, receiver 1, which is connected to the same hybrid junction terminal as transmitter 12, would always be tuned to receive the same polarization as was transmitted. Often this type of reception is desirable, but in some cases better target resolution may be obtained by tuning one of the receivers for a particular polarization other than the transmitted or its cross-polarized component.

A better understanding of the desirability of independent tuning of the transmitted and received polarization may be had from referring to the diagrams of FIG. 3. FIG. 3(a) represents an elliptically polarized wave transmitted from antenna 13. It may be characterized by three features; the ellipticity e which is the ratio of the major axis y to the minor axis x; the orientation which is designated by the angle between the major axis and the horizontal; and the rotational sense which is indicated as clockwise by the arrow. FIG. 3(1)) represents the orthogonal component of the polarization of FIG. 3(a). This orthogonal or cross-polarized component has the same ellipticity but has an opposite rotational sense and the orientation of the major axis is displaced 90. FIG. 3(0) represents a single bounce reflected wave produced by the polarization of FIG. 3(a). A single bounce reflected wave, as the name suggests, is one which has been reflected back to the transmitter after undergoing a refiection from a single surface which is dimensionally large compared to a wavelength. A double bounce wave, i.e., one undergoing reflection from two surfaces, is normally indicative of a reflecting structure with inside corners (or dihedral corner refiectors) and is a mirror image of the single bounce wave.

If there is no provision for independent tuning, receiver 1 would receive the polarization of FIG. 3(a) and receiver 2, the polarization of FIG. 3(1)). Therefore, the single bounce reflected wave of FIG. 3(a) would be re ceived partially by each receiver because of its dissimilarity to the tuned polarization of either receiver. It may be desirable to tune one receiver only to receive the single bounce reflected waves. With the complete control provided by the four phase shifters, a reflected wave of any polarization may be received wholly or in part by either receiver.

There are numerous display methods which may be used to take advantage of the information obtained by receivers 1 and 2. My co-pending application No. 188,459 filed Oct. 4, 1950, now Patent No. 3,048,837, on a Signal Display System discloses several suitable display means, one involving the use of two cathode ray tubes with screens of different color and their images superimposed on a common screen. Another display method disclosed therein involves the use of a medium intensity background on a cathode ray tube with the two receivers controlling the intensity with opposite polarities so that one sense polarization would darken the screen and its cross-polarized component would brighten the screen. Other display systems are readily apparent to employ the additional information obtained by the two receivers to increase target discrimination.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. Apparatus for transmitting any type of polarized electromagnetic waves comprising means for dividing a signal into two equal signal components of like time phase, a hybrid junction including a first and second pair of symmetrical terminal points, a first and second transmission means for conducting each said signal component to a terminal of said first pair of symmetrical terminals, said first transmission means including phase displacement means, two antennas capable of producing a resultant electromagnetic wave dependent on the time phase and amplitude relations of energization, and first and second connecting means for connecting each of said second pair of symmetrical terminals to one of said antennas, said first connecting means including a phase displacement means for varying the time phase between said signal components to any predetermined value.

2. Apparatus for transmitting any type of polarized electromagnetic waves comprising means for dividing a signal into two equal signal components of like time phase, a hybrid junction including a first and second pair of symmetrical terminal points, a first and second transmission means for conducting each said signal component to a terminal of said first pair of symmetrical terminals, said first transmission means including variable phase delay means producing from 0 to phase delay, two antennas capable of producing a resultant electromagnetic wave dependent on the time phase and amplitude relations of energization, and first and second connecting means for connecting each of said second pair of symmetrical terminals to one of said antennas, said first connecting means including a variable phase delay means producing from O to 180 phase delay.

3. Apparatus for transmitting and receiving any selected electromagnetic wave polarization and receiving the cross-polarized component of said selected polarization comprising a transmitter, a pair of receivers, a first and a second hybrid junction each having a first and a second pair of symmetrical terminals, transmission means connecting said transmitter and one of said receivers to one terminal of said first pair of terminals of said first junction, transmission means connecting the other of said receivers to the other terminal of said first pair of terminals, transmission means connecting each terminal of said second pair of terminals of said first hybrid junction to respective terminals of a first symmetrical pair in said second hybrid junction, one of said terminal connecting means including a phase shifter, antenna means having two spatially disposed radiating means, and transmission means connecting the second pair of symmetrical terminals on said second hybrid junction to said radiating means, one of said transmission means including a phase shifter.

4. Apparatus for transmitting and receiving any selected electromagnetic wave polarization and receiving the crosspolarized component of said selected polarization comprising a transmitter, a pair of receivers, a first and a second hybrid junction each having a first and a second pair of symmetrical terminals, transmission means connecting said transmitter and one of said receivers to one terminal of said first pair of terminals of said first junction, transmission means connecting the other of said receivers to the other terminal of said first pair of terminals, transmission means connecting each terminal of said second pair of terminals of said first hybrid junction to respective terminals of a first symmetrical pair in said second hybrid junction, one of said terminal connecting means including a phase shifter of variable phase delay between 0 and 180, antenna means having two spatially disposed radiating means, and transmission means connecting the second pair of symmetrical terminals on said second hybrid junction o said radiating means, one of said transmission means in- :luding a phase shifter of variable phase delay between and 180.

5. Apparatus for transmitting and receiving any selected :lectromagnetic wave polarization and receiving the cross- Jolarized component of said selected polarization comprisng a transmitter, a pair of receivers, a first and a second iybrid junction each having a first and a second pair of ;ymmetrical terminals, transmission means connecting said ransmitter and one of said receivers to one terminal of said first pair of terminals of said first junction, transmission means connecting the other of said receivers to the other :erminal of said first pair of terminals, transmission means connecting each terminal of said second pair of terminals of said first hybrid junction to respective terminals of a first symmetrical pair in said second hybrid junction, one of said terminal connecting means including a phase shifter of variable phase delay between 0 and 180, antenna horn means, horizontal and vertical probe radiating means disposed in said horn, and transmission means connecting the second pair of symmetrical terminals on said second hybrid junction to said radiating means, one of said transmission means including a phase shifter of variable phase delay between 0 and 180.

6. Apparatus for transmitting an electromagnetic wave of any predetermined type of polarization and receiving any predetermined type and also the cross-polarized component of the said predetermined received wave comprising antenna means having two spatially disposed radiating means, a first hybrid junction having a first and second pair of symmetrical terminals, transmission means connecting each of said radiating means to one terminal of said first pair of symmetrical terminals, one of said transmission means including two parallel transmission paths each with an adjustable phase displacement means, one of said parallel paths including a transmitted wave rejection device and the other including a received wave rejection device, a second hybrid junction having a first and second pair of symmetrical terminals, transmission means connecting each of said second pair of symmetrical terminals of said first hybrid junction to a terminal of said first pair of symmetrical terminals of said second hybrid junction, one of said last mentioned transmission means including two parallel transmission paths each with an adjustable phase displacement means, one of said parallel paths including a transmitted wave rejection device and the other including a received wave rejection device, a pair of receiver means each of which is connected to one terminal of said second pair of terminals of said second hybrid junction, and transmitter means connected to one of said second pair of terminals of said second hybrid junction.

7. Apparatus for transmitting an electromagnetic wave of any predetermined type of polarization and receiving any predetermined type and also the cross-polarized component of the said predetermined received wave comprising antenna means having two radiating means disposed in spaced quadrature, a first hybrid junction having a first and second pair of symmetrical terminals, transmission means connecting each of said radiating means to one terminal of said first pair of symmetrical terminals, one of said transmission means including two parallel transmission paths each with an adjustable phase displacement means, one of said parallel paths including transmitted Wave rejection means and the other including received wave rejection means, a second hybrid junction having a first and second pair of symmetrical terminals, transmission means connecting each of said second pair of symmetrical terminals of said first hybrid junction to a terminal of said first pair of symmetrical terminals of said second hybrid junction, one of said last mentioned transmission means including two parallel transmission paths each with an adjustable phase displacement means, one of said parallel paths including transmitted wave rejection means and the other including received ware rejection means, a pair of receiver means each of which is connected to one terminal of said second pair of terminals of said second hybrid junction, and transmitter means connected to one of said second pair of terminals of said second hybrid junction.

References Cited UNITED STATES PATENTS 2,273,161 2/1942 Usselman 343-100.3 2,443,612 6/1948 Fox 250-6.421 2,607,849 8/1952 Purcell '343-5 1,853,021 4/1932 Alexanderson 343-1003 2,312,799 3/1943 Carter 343-1003 2,619,635 11/1952 Chait.

2,377,902 6/ 1945 Relson 343-106 2,687,520 8/1954 FOX 34316 X RICHARD A. FARLEY, Primary Examiner.

NORMAN H. EVANS, ARTHUR GAUSS,

Examiners.

A. K. GEER, R. D. BENNETT, M. F. HUBLER,

Assistant Examiners. 

1. APPARATUS FOR TRANSMITTING ANY TYPE OF POLARIZED ELECTROMAGNETIC WAVES COMPRISING MEANS FOR DIVIDING A SIGNAL INTO TWO EQUAL SIGNAL COMPONENTS OF LIKE TIME PHASE, A HYBRID JUNCTION INCLUDING A FIRST AND SECOND PAIR OF SYMMETRICAL TERMINAL POINTS, A FIRST AND SECOND TRANSMISSION MEANS FOR CONDUCTING EACH SAID SIGNAL COMPONENT TO A TERMINAL OF SAID FIRST PAIR OF SYMMETRICAL TERMINALS, SAID FIRST TRANSMISSION MEANS INCLUDING PHASE DISPLACEMENT MEANS, TWO ANTENNAS CAPABLE OF PRODUCING A RESULTANT ELECTROMAGNETIC WAVE DEPENDENT ON THE TIME PHASE AND AMPLITUDE RELATIONS OF ENERGIZATION, AND FIRST AND SECOND 